Corolla tube formation in the Tubiflorae and Gentianales

Corolla tube formation was investigated anatomically for 22 species of the Polemoniaceae, Convolvulcaeae, Boraginaceae, Verbenaceae, Buddlejaceae. Scrophulariaceae, Gentianaceae, Menyanthaceae and Asclepiadaceae. The corolla tbe formation is basically similar among species, except for the cases ofNymphoides, Dichondra andCuscuta. The petal bases extend laterally to the interprimordial regions, the upward growth occurring at those regions just beside the petal bases, and connect mutually at the back of stamen primordia. The upward growth at the connected regions co-opeates with the growth of the expanding petal margins, resulting in the formation of the upper portion of the corolla tube. How-ever, developmental patterns are not always similar. InSwertia, Nymphoides andMenyanthes, the upward growth at the connected regions is meager. InDichondra andCuscuta, the mutual connection of petal bases is not seen. The lower portion of the corolla tube is formed by the elongation of the common base of petal and stamen primordia, resulting in the formation of the epipetalous condition of stamens, except for the case ofNymphoides. InNymphoides, the lower portion of the corolla tube results from the cup-like structure formed on the floral meristem before the initiation of petal primordia.